Memory modules are used, for example, to provide main memory for a processor-based data processing architecture.
FIG. 3 shows a plan view of an exemplary memory module 2 that can be tested with the apparatus according to the invention. A memory module 2 of this type comprises a circuit board 28 and also at least two memory chips 26a–26m arranged thereon. A plurality of memory chips 26a–26m, for example 8, 10, 18 or 36, are usually applied on a circuit board or printed circuit board 28 of this type, it being possible for both the front side and the rear side of the circuit board to be populated. Examples of memory chips 26 comprise SDRAM or DDR SDRAM (“Double Data Rate Synchronous Dynamic Random Access”), memory chips and examples of modules comprise DIMM (“Dual Inline Memory Module”) SDRAM or DIMM DDR SDRAM modules.
In the example shown, the front and rear sides of the circuit board are provided with contacts 27a to 27n at one side of the circuit board. By way of example, a total of 168 or 184 or an arbitrary number of contacts 27 may be provided via which signals are exchanged with the motherboard. The assignment as to which of the individual contacts of the memory module 2 are data, address or command lines can be gathered from the data sheets available with respect to the memory modules.
FIG. 3 also shows the electrical connections 30 associated with each memory chip and the respective mode registers 29a to 28m. 
For operation, the memory module is inserted into a dedicated motherboard slot 19 and can be used as a main memory component as intended after configuration has been effected by the motherboard.
During the production of semiconductor components, such as DRAMs for example, the individual integrated circuits are usually tested while still at the wafer level by emplacement of measuring tips. The wafers are singulated into chips and the functioning chips are mounted, contact-connected and encapsulated in suitable housings. Afterward, a plurality of chips are combined to form modules by being applied on a common printed circuit board. For the functional test at the chip level, there are generally specific test circuits that are used in order to carry out the envisaged functional tests.
Particular importance is accorded to the subsequent application tests or the so-called application analysis. The interaction between the motherboard of a computer and module is examined during the application analysis. In this case, the modules in the application often behave differently than expected from the component analysis. In particular, the individual chips in the isolated state exhibit nothing conspicuous whatsoever, while the modules during the application analysis only function in certain motherboards and not in the others.
The examination of the cause of fault is problematic since generally the interaction between motherboard and module cannot be examined without intervening in the basic functions of the motherboard, whereby the measurement results are in turn corrupted.
The examination of the cause of a fault is furthermore made more difficult by the fact that, by virtue of the module being incorporated into the system, the individual subelements of the module can be accessed only with very great difficulty.
The analysis has hitherto been restricted to adjusting reference voltages on the motherboard or to adjusting the BIOS (“basic input output system”), connecting in resistances and capacitances on signal lines. Since the motherboard can only be operated in a well-defined and prescribed operating mode, however, it is not possible to carry out tests, which put the memory modules into an extreme state. By way of example, there is no known possibility of altering the timing of the chips situated on the module, of applying particularly high voltages or else, for example in the case of memory modules, of carrying out tests for determining the storage time, since the motherboard is not designed to operate with such extreme states and, therefore, does not actually permit the latter at all.
An analysis socket is commercially available which is soldered onto the motherboard and permits the module to be operated independently after the start-up of the system. Since most faults occur during the start-up of the system, the analysis socket is only of limited use. What is more, the module to be tested cannot be accessed directly from the conventional analysis socket. The module can only be accessed via the motherboard.
A further problem consists in the fact that in the booting phase, in which most application problems usually occur, a mode register set is performed by means of which the bits that specify the operating state of the individual chips are set to predetermined values. The individual chips and thus the module are thereby put into a normal application state. Accordingly, it is not possible to test a module during the start-up of the computer in a test mode. For the application engineer, however, it would precisely be of interest to put the chips into a test mode prior to the booting phase being performed, in order to examine the influence of the test modes on the booting process. This would enable application tests to be performed particularly rapidly and effectively.